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Analysis of photon emission induced by light and heavy ions in time-of-flight medium energy ion scattering
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.ORCID iD: 0000-0002-5815-3742
2018 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 417, p. 75-80Article in journal (Refereed) Published
Abstract [en]

We present a systematic analysis of the photon emission observed due to impact of pulsed keV ion beams in time-of-flight medium energy ion scattering (ToF-MEIS) experiments. Hereby, hydrogen, helium and neon ions served as projectiles and thin gold and titanium nitride films on different substrates were employed as target materials. The present experimental evidence indicates that a significant fraction of the photons has energies of around 10 eV, i.e. on the order of typical valence and conduction band transitions in solids. Furthermore, the scaling properties of the photon emission with respect to several experimental parameters were studied. A dependence of the photon yield on the projectile velocity was observed in all experiments. The photon yield exhibits a dependence on the film thickness and the scattering angle, which can be explained by photon production along the path of the incident ion through the material. Additionally, a strong dependence on the projectile type was found with the photon emission being higher for heavier projectiles. This difference is larger than the respective difference in electronic stopping cross section. The photon yield shows a strong material dependence, and according to a comparison of SiO2 and Si seems to be subject to matrix effects. (C) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV , 2018. Vol. 417, p. 75-80
Keywords [en]
Photons, Deep UV, TOF-MEIS, Au
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:uu:diva-348917DOI: 10.1016/j.nimb.2017.08.005ISI: 000426030500014OAI: oai:DiVA.org:uu-348917DiVA, id: diva2:1201301
Conference
15th International Conference on Particle Induced X-ray Emission (PIXE), APR 02-07, 2017, Split, CROATIA
Funder
Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, 821-2012-5144Available from: 2018-04-25 Created: 2018-04-25 Last updated: 2020-05-04Bibliographically approved
In thesis
1. Electronic excitation, luminescence and particle emission: Studying ion-induced phenomena in ToF-MEIS
Open this publication in new window or tab >>Electronic excitation, luminescence and particle emission: Studying ion-induced phenomena in ToF-MEIS
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Medium energy ion scattering (MEIS) is an experimental technique for the high-resolution depth profiling of thin films. Commonly, ions with energies between several ten to a few hundred keV are employed as probes, and backscattered particles are detected. Apart from scattering, keV ions can upon their interaction with matter induce luminescence, electron emission and the sputtering of neutrals and ions. However, research on this secondary particle emission in the medium energy regime is scarce. Thus, this thesis aims to perform a systematic analysis of 1) ion-induced photon emission and 2) the sputtering of positive ions in a time-of-flight (ToF) MEIS set-up. A significant fraction of photons exhibits energies of only a few eV, which is on the order of typical valence transitions in solids. The dependence of the photon yield on several experimental parameters is studied. By analysing the dependence on the employed geometry, it is concluded that photons are produced along the whole trajectory of the incident ion. Furthermore, the photon yield shows a strong material dependence, which seems to be subject to matrix effects. To study the sputtering process, mass spectrometry was integrated into an existing ToF-MEIS set-up. The secondary ions exhibit very low initial kinetic energies and, therefore, need to be accelerated by a sufficiently high voltage. Then, atomic and molecular ions originating both from the employed target material and surface contaminations can be detected. Whereas experimental evidence suggests a predominantly electronic sputtering process for species adsorbed to the surface, target bulk constituents seem to be sputtered by nuclear collision cascades. 

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2018. p. 42
Keywords
TOF-MEIS, ion beam analysis, deep UV, desorption, electronic sputtering, TiN
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-351261 (URN)
Presentation
2018-05-24, Å4006, Ångströmlaboratoriet, Uppsala, 14:00 (English)
Opponent
Supervisors
Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-22Bibliographically approved
2. Beyond scattering – what more can be learned from pulsed keV ion beams?
Open this publication in new window or tab >>Beyond scattering – what more can be learned from pulsed keV ion beams?
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Interactions of energetic ions with matter govern processes as diverse as the influence of solar wind, hadron therapy for cancer treatment and plasma-wall interactions in fusion devices, and are used for controlled manipulation of materials properties as well as analytical methods. The scattering of ions from target nuclei and electrons does not only lead to energy deposition, but can induce the emission of different secondary particles including electrons, photons, sputtered target ions and neutrals as well as nuclear reaction products. In the medium-energy regime (ion energies between several ten to a few hundred keV), ions are expected to primarily interact with valence electrons. Dynamic electronic excitations are, however, not understood in full detail, and remain an active field of experimental and theoretical research. In addition, whereas scattered ions are employed for high-resolution depth profiling in medium energy ion scattering (MEIS), research on secondary particle emission in this regime is scarce.

This thesis explores possibilities to experimentally study ion-solid interactions in the medium-energy regime beyond a backscattering approach. The capability for detection of electrons, photons and sputtered ions was integrated into the time-of-flight (ToF-) MEIS set-up at Uppsala University. Additionally, transmission of ions in combination with crystalline samples was employed to study impact-parameter dependent electronic excitations. In all cases, the use of pulsed ion beams with nanosecond pulse widths proves to be imperative for achieving energy measurements with sufficient resolution as well as low doses for non-destructive interactions even with sensitive samples.

Trajectory-dependent energy loss of various ions in Si(100) was studied. For all ions heavier than protons, experimental evidence shows that, if close collisions are not suppressed by channelling, consequent charge-exchange events increase the mean charge state of the ion and heavily influence the experienced energy loss. Furthermore, measurements of electron emission are presented. For medium-energy ions, electrons emitted in forward direction from carbon foils exhibit energies between 10 and 400 eV. Scaling with ion velocity indicates binary collisions as the primary energy transfer mechanism. Detected photons also have energies of a few eV, i.e. on the order of typical valence transitions in solids. For photon emission, pronounced chemical matrix effects are observed. Finally, the sputtering process at medium energies was studied. Target bulk constituents exhibit similar behaviour as known from established methods at lower energies, i.e. sputtering by nuclear collision cascades. In contrast, the desorption of surface species seems to be governed by electronic energy transfer mechanisms.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 90
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1945
Keywords
Charge exchange, Deep UV photons, Electron emission, Silicon, Sputtering, TOF-MEIS
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-409892 (URN)978-91-513-0964-4 (ISBN)
Public defence
2020-06-12, Polhelmsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2020-05-20 Created: 2020-05-04 Last updated: 2020-05-20

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Lohmann, SvenjaSortica, Mauricio A.Paneta, ValentinaPrimetzhofer, Daniel

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